Spatially-controlled synthesis of palladium—rhodium hetero-nanostructures
In a method of generating a nanocrystal with a core-frame structure, a seed crystal, including a first substance, is exposed to a capping agent. The seed nanocrystal has a plurality of first portions that each has a first characteristic and a plurality of second portions that each has a second characteristic, different from the first characteristic. The capping agent has a tendency to adsorb to portions having the first characteristic and has a tendency not to adsorb to portions having the second characteristic. As a result, a selectively capped seed nanocrystal is generated. The selectively capped seed nanocrystal is exposed to a second substance that has a tendency to nucleate on the plurality of second portions and that does not have a tendency to nucleate on portions that have adsorbed the capping agent, thereby generating a frame structure from the plurality of second portions of the seed nanocrystal.
1. A method of generating a nanocrystal with a core-frame structure, comprising the steps of:
(a) exposing a seed crystal, comprising a first substance, to a capping agent, the seed nanocrystal having a plurality of first portions having a first characteristic and a plurality of second portions having a second characteristic, different from the first characteristic, wherein the capping agent has a tendency to adsorb to portions having the first characteristic and having a tendency not to adsorb to portions having the second characteristic, thereby generating a selectively capped seed nanocrystal; and
(b) exposing the selectively capped seed nanocrystal to a second substance that has a tendency to nucleate on the plurality of second portions and that does not have a tendency to nucleate on portions that have adsorbed the capping agent, thereby generating a frame structure from the plurality of second portions of the seed nanocrystal.
2. The method of claim 1 , further comprising the step of etching the seed nanocrystal with an etchant that is configured to remove the first substance from the frame structure.
3. The method of claim 1 , wherein the plurality of second portions comprise a selected family of edges and corners.
4. The method of claim 1 , wherein the plurality of first portions comprise {100} families of crystal facets.
5. The method of claim 4 , wherein the seed nanocrystal has a cubic shape and wherein the selected family of crystal facets comprises a {100} family of facets.
6. The method of claim 4 , wherein the seed nanocrystal has a cuboctahedral shape.
7. The method of claim 6 , wherein the plurality of second portions comprises {111} families of facets.
8. The method of claim 1 , wherein the first substance comprises Pd and wherein the second substance comprises a salt precursor to Rh.
9. The method of claim 8 , wherein the salt precursor to Rh comprises Na 3 RhCl 6 .
10. The method of claim 1 , further comprising the step of selecting the first substance and the second substance so that the frame structure is configured to be used as a catalyst in a predetermined catalytic reaction.
11. The method of claim 1 , wherein the capping agent comprises a solution including halide ions.
12. The method of claim 11 , wherein the halide ions include Br − ions.
13. The method of claim 1 , wherein the seed nanocrystal comprises a nanocrystal selected from a group consisting of: a cubic nanocrystal; an octahedral nanocrystal; and a cuboctahedral nanocrystal.
14. A method of generating a cubic frame structure, comprising the steps of:
(a) exposing a plurality of Pd nanocrystals having a cubic shape to a solution including Br − ions for a sufficient time so that the Br − ions are adsorbed to a {100} family of crystal facets on the Pd nanocrystals so as to form selectively capped nanocrystals;
(b) adding a solution including a salt precursor to Rh to the selectively capped nanocrystals at a rate that causes Rh to nucleate from edges and corners of the Pd nanocrystals so as to generate a frame structure affixed to the edges and corners of the Pd nanocrystals; and
(c) etching Pd from the Pd nanocrystals so as to leave a plurality of cubic Rh frame structures.
15. The method of claim 14 , wherein the salt precursor to Rh includes Na 3 RhCl 6 .
16. A method of generating a cuboctahedral core-frame structure, comprising the steps of:
(a) exposing a plurality of Pd nanocrystals having a cuboctahedral shape to a solution including Br − ions for a sufficient time so that the Br − ions are adsorbed to a {100} family of crystal facets on the Pd nanocrystals so as to form selectively capped nanocrystals; and
(b) adding a solution including a salt precursor to Rh to the selectively capped nanocrystals at a rate that causes Rh to nucleate from a {111} family of crystal facets on the Pd nanocrystals so as to generate a frame structure affixed to the {111} family of crystal facets of the Pd nanocrystals.
17. The method of claim 16 , further comprising the step of etching Pd from the Pd nanocrystals so as to leave a plurality of cuboctahedral Rh frame structures.
18. The method of claim 16 , wherein the salt precursor to Rh includes Na 3 RhCl 6 .